Acromegaly

Acromegaly (from Greek akros "high" and megalos "large" - extremities enlargement) is a is a hormonal disorder that results when the pituitary gland produces excess growth hormone (hGH). Most commonly it is a benign hGH producing tumor derived from a distinct type of cells (somatotrophs) and called pituitary adenoma. It most commonly affects middle-aged adults and can result in serious illness and premature death. In children the related condition is called gigantism, because long bones can still grow. The disease because of its slow and often insidious onset, is frequently not diagnosed correctly.

Features that result from high level of hGH or expanding tumor include:

Soft tissue swelling of the hands and feet (early sign)
Brow and lower jaw protrusion (enlarging jaw and hat size)
Enlarging hands (ring size)
Enlarging feet (shoe size)
Arthritis and carpal tunnel syndrome
Teeth spacing increase
Heart failure (major medical problem).
Compression of the optic chiasm leading to loss of vision in the outer visual fields.
diabetes mellitus
hypertension

Table of contents

1 Causes
2 Treatment

2.1 Surgery
2.2 Drug Therapy
2.3 Radiation Therapy

Causes

In over 90 percent of acromegaly patients, the overproduction of GH is caused by a benign tumor of the pituitary gland, called an adenoma. These tumors produce excess GH and, as they expand, compress surrounding brain tissues, such as the optic nerves. This expansion causes the headaches and visual disturbances that are often symptoms of acromegaly. In addition, compression of the surrounding normal pituitary tissue can alter production of other hormones, leading to changes in menstruation and breast discharge in women and impotence in men.

There is a marked variation in rates of GH production and the aggressiveness of the tumor. Some adenomas grow slowly and symptoms of GH excess are often not noticed for many years. Other adenomas grow rapidly and invade surrounding brain areas or the sinuses, which are located near the pituitary. In general, younger patients tend to have more aggressive tumors.

Most pituitary tumors arise spontaneously and are not genetically inherited. Many pituitary tumors arise from a genetic alteration in a single pituitary cell which leads to increased cell division and tumor formation. This genetic change, or mutation, is not present at birth, but is acquired during life. The mutation occurs in a gene that regulates the transmission of chemical signals within pituitary cells; it permanently switches on the signal that tells the cell to divide and secrete GH. The events within the cell that cause disordered pituitary cell growth and GH oversecretion currently are the subject of intensive research.

In a few patients, acromegaly is caused not by pituitary tumors but by tumors of the pancreas, lungs, and adrenal glands. These tumors also lead to an excess of GH, either because they produce GH themselves or, more frequently, because they produce GHRH, the hormone that stimulates the pituitary to make GH. In these patients, the excess GHRH can be measured in the blood and establishes that the cause of the acromegaly is not due to a pituitary defect. When these non-pituitary tumors are surgically removed, GH levels fall and the symptoms of acromegaly improve.

In patients with GHRH-producing, non-pituitary tumors, the pituitary still may be enlarged and may be mistaken for a tumor. Therefore, it is important that physicians carefully analyze all "pituitary tumors" removed from patients with acromegaly in order not to overlook the possibility that a tumor elsewhere in the body is causing the disorder.

Because bromocriptine can be taken orally, it is an attractive choice as primary drug or in combination with other treatments. However, bromocriptine lowers GH and IGF-1 levels and reduces tumor size in less than half of patients with acromegaly. Some patients report improvement in their symptoms although their GH and IGF-1 levels still are elevated.

The second medication used to treat acromegaly is octreotide (Sandostatin). Octreotide is a synthetic form of a brain hormone, somatostatin, that stops GH production. This drug must be injected under the skin every 8 hours for effective treatment. Most patients with acromegaly respond to this medication. In many patients, GH levels fall within one hour and headaches improve within minutes after the injection. Several studies have shown that octreotide is effective for long-term treatment. Octreotide also has been used successfully to treat patients with acromegaly caused by non-pituitary tumors.

Because octreotide inhibits gastrointestinal and pancreatic function, long-term use causes digestive problems such as loose stools, nausea, and gas in one third of patients. In addition, approximately 25 percent of patients develop gallstones, which are usually asymptomatic. In rare cases, octreotide treatment can cause diabetes. On the other hand, scientists have found that in some acromegaly patients who already have diabetes, octreotide can reduce the need for insulin and improve blood sugar control.

Radiation Therapy

Radiation therapy has been used both as a primary treatment and combined with surgery or drugs. It is usually reserved for patients who have tumor remaining after surgery. These patients often also receive medication to lower GH levels. Radiation therapy is given in divided doses over four to six weeks. This treatment lowers GH levels by about 50 percent over 2 to 5 years. Patients monitored for more than 5 years show significant further improvement. Radiation therapy causes a gradual loss of production of other pituitary hormones with time. Loss of vision and brain injury, which have been reported, are very rare complications of radiation treatments.

No single treatment is effective for all patients. Treatment should be individualized depending on patient characteristics, such as age and tumor size. If the tumor has not yet invaded surrounding brain tissues, removal of the pituitary adenoma by an experienced neurosurgeon is usually the first choice. After surgery, a patient must be monitored for a long time for increasing GH levels. If surgery does not normalize hormone levels or a relapse occurs, a doctor will usually begin additional drug therapy. The first choice should be bromocriptine because it is easy to administer; octreotide is the second alternative. With both medications, long-term therapy is necessary because their withdrawal can lead to rising GH levels and tumor re-expansion. Radiation therapy is generally used for patients whose tumors are not completely removed by surgery; for patients who are not good candidates for surgery because of other health problems; and for patients who do not respond adequately to surgery and medication.

Largely adopted from http://www.niddk.nih.gov/health/endo/pubs/acro/acro.htm